Atomistic simulations were used to investigate how the stress required for homogeneous nucleation of partial dislocations in single crystal copper under uniaxial loading changed as a function of crystallographic orientation. Molecular dynamics was employed based upon an embedded-atom method potential for Cu at 10 and 300K. Results indicated that non-Schmid parameters were important for describing the calculated dislocation nucleation behavior for single crystal orientations under tension and compression. A continuum relationship was presented that incorporates Schmid and non-Schmid terms to correlate the nucleation stress over all tensile axis orientations within the stereographic triangle. Simulations investigating the temperature dependence of homogeneous dislocation nucleation yield activation volumes of ≈0.5 to 2b3 and activation energies of about 0.30eV. For uniaxial compression, full dislocation loop nucleation was observed, in contrast to uniaxial tension. One of the main differences between uniaxial tension and compression was how the applied stress was resolved normal to the slip plane on which dislocations nucleate—in tension, this normal stress was tensile, and in compression, it was compressive. Last, the tension–compression asymmetry was examined as a function of loading axis orientation. Orientations with a high resolved stress normal to the slip plane on which dislocations nucleate had a larger tension–compression asymmetry with respect to dislocation nucleation than those orientations with a low resolved normal stress. The significance of this research was that the resolved stress normal to the slip plane on which dislocations nucleate played an important role in partial (and full) dislocation loop nucleation in face-centered cubic Cu single crystals.

Influence of Single Crystal Orientation on Homogeneous Dislocation Nucleation under Uniaxial Loading. M.A.Tschopp, D.L.McDowell: Journal of the Mechanics and Physics of Solids, 2008, 56[5], 1806-30